Method for etching a compound semiconductor, a semi-conductor laser device and method for producing the same

ABSTRACT

An etching method for performing dry-etching on a III-V group compound semiconductor or a II-VI group compound semiconductor in a dry-etching apparatus comprising a plasma source for creating a plasma of density of about 10 10  cm -3  or greater, using a mixed gas containing a gas including a halogen element and a gas including nitrogon. The etching conditions are as follows: (a flow rate of the gas containing said halogen gas)/(a flow rate of said nitrogen gas) ≧1; and an internal pressure during etching reaction is about 1 mTorr or greater.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a compound semiconductor and a methodfor producing the same. More particularly, the present invention relatesto a dry-etching method for a III-V group or II-VI group compoundsemiconductor, and to a semiconductor laser device fabricated thereby.

2. Description of the Related Art

As a conventional dry-etching technique for a compound semiconductor, amethod described in Japanese Laid-Open Patent Publication No. 7-66175 isknown in the art. In this method, dry-etching is performed on anIn-containing compound semiconductor by using ECR-RIBE (ElectronCyclotron Resonance-Reactive Ion Beam Etching) apparatus with auxiliarycoil reducing a divergence of magnetic field. In the ECR-RIBE apparatus,a primary coil and an auxiliary coil are provided so that the divergenceof magnetic field in the vicinity of the sample to be etched isinhibited. In this method, chlorine, helium and nitrogen are used as theetching gas. With the flow ratio of the chlorine/nitrogen gases beingequal to one or less and the internal pressure being equal to 0.5 mTorr,a cross-section which is vertical with respect to the etching mask and asmooth etching surface are obtained.

According to the above-mentioned publication, when the gas is suppliedwith the chlorine gas/nitrogen gas ratio being equal to one or less, theproduction of chlorine radicals is inhibited and the etching due tochlorine ions becomes more predominant over the etching due to chlorineradicals. This makes it possible that ions having energy as low asseveral tens of eV can be used and a balance of evaporation of achloride of In and a chloride of P can still be achieved. As a result,etching which is capable of obtaining a cross-section which is verticalwith respect to the etching mask, and of obtaining a smooth etchingsurface can be realized.

Conventionally, the dry-etching of compound semiconductor had problemsassociated with roughness of the etching surface due to a largedifference in vapor pressures between the reactant of a III groupelement and the etching gas and the reactant of a V group element andthe etching gas or with difficulty in controlling cross-sectionalshapes.

Dry-etching technology disclosed in the above-mentioned publication alsointended to solve these problems. In this technology, nitrogen gas isadded so that chlorine gas is decomposed and the amount of chlorineradicals created with chlorine ions is kept below 1/3 of the totalamount of chlorine radicals and chlorine ions, thereby solving theabove-mentioned problems. Also realized in the above-mentionedtechnology is that a pressure inside the reaction chamber is made equalto 0.5 mTorr or less in order to minimize the production of chlorineradicals. This results in desorption velocities in equilibrium of thechloride of In and the chloride of P. A feature of the above-mentionedtechnology is that the etching is carried out under conditions whichminimize the concentration of chlorine radicals. The above-mentionedpublication does not show quantitative data concerning the amount ofchlorine ions produced and the etching characteristics.

Moreover, if a sample to be etched contains Al, then Al₂ O₃ is formedwith moisture remaining in the reaction chamber, thereby preventing theetching or greatly reducing the etching rate.

SUMMARY OF THE INVENTION

According to one aspect of the present invention, in an etching methodfor performing dry-etching on a III-V group compound semiconductor or aII-VI group compound semiconductor in a dry-etching apparatus includinga plasma source for creating a plasma of density of about 10¹⁰ cm⁻³ orgreater, using a mixed gas containing a gas including a halogen elementand a gas including nitrogen, (a flow rate of the gas containing thehalogen gas)/(a flow rate of the nitrogen gas) ≧about 1, and an internalpressure during etching reaction is about 1 mTorr or greater.

In one embodiment of the present invention, ions created in the plasmasource are accelerated, and a sample is etched by kinetic energy of theaccelerated ions while a sample surface is being heated.

In one embodiment of the present invention, ions created in the plasmasource are accelerated. Only a portion of the sample containing a II-VIgroup compound in the vicinity of the surface is heated by kineticenergy of the accelerated ions, and a support for the sample is cooled.

In one embodiment of the present invention, etching is performed while asample holder is heated.

In one embodiment of the present invention, an etching method furtherincludes the steps of: performing a first dry-etching wherein ionscreated in the plasma source are accelerated by a first acceleratingvoltage; and performing a second dry-etching, after the firstdry-etching, wherein ions created in the plasma source are acceleratedby a second accelerating voltage. The second accelerating voltage islarger than the first accelerating voltage.

In one embodiment of the present invention, an etching method furtherinclude a step of performing wet-etching.

In one embodiment of the present invention, the dry-etching apparatusincludes a radical beam source and an ion beam source, and a density ofradicals created in the radical beam source and a density of ionscreated in the ion beam source are independently controlled.

In one embodiment of the present invention, the compound semiconductoris formed of Al_(x) Ga_(y) In_(1-x-y) P (0<x≦1, 0≦y≦1).

In one embodiment of the present invention, the compound semiconductoris formed above an off-substrate.

According to another aspect of the present invention, an etching methodfor performing dry-etching on a III-V group compound semiconductor or aII-VI group compound semiconductor in a dry-etching apparatus includinga plasma source for creating a plasma of density of about 10¹⁰ cm⁻³ orgreater, using a mixed gas containing a gas including halogen elementand a gas including nitrogen, includes the steps of: performing a firstdry-etching with a halogen ion density being made larger than a halogenradical density; and performing a second dry-etching with a halogen iondensity being made smaller than a halogen radical density.

According to yet another aspect of the present invention, an etchingapparatus includes a radical beam source, an ion beam source, a reactionchamber having the radical beam source and the ion beam source connectedthereto, a sample support provided inside the reaction chamber and aload lock chamber.

According to still another aspect of the present invention, a method forproducing a semiconductor laser device includes the steps of:epitaxially growing at least one compound semiconductor layer on asemiconductor substrate; forming a patterned mask on the at least onecompound semiconductor layer; performing etching on the at least onecompound semiconductor layer, using the patterned mask, by any one ofthe etching methods described above so as to form a ridge stripe; andburying the ridge stripe with compound semiconductor.

In one embodiment of the present invention, the substrate is amisoriented substrate; the at least one compound semiconductor layerincludes an active layer, an n-AlGaInP cladding layer and p-AlGaInPcladding layer, the n-AlGaInP cladding layer and the p-AlGaInP claddinglayer interposing the active layer; and the ridge stripe contains thep-AlGaInP layer.

In one embodiment of the present invention, the p-AlGaInP cladding layerhas a p-AlGaInP first cladding layer and a p-AlGaInP second claddinglayer, and an etching stopper layer is formed between the first claddinglayer and the second cladding layer.

In one embodiment of the present invention, a layer for monitoring anetched amount of the p-AlGaInP second cladding layer is formed withinthe p-AlGaInP second cladding layer.

According to still another aspect of the present invention, asemiconductor laser device includes: a substrate; and a ridge stripeformed on the substrate and including an active layer, an n-claddinglayer and p-cladding layer, the n-cladding layer and the p-claddinglayer interposing the active layer. The ridge stripe has a laser unitwhich lases and a tip portion having a tapered shape. An angle formedinside the ridge stripe by a bottom surface of the ridge stripe and aside surface of the ridge stripe is in the range of about 60° and about90°.

According to still another aspect of the present invention, asemiconductor laser device includes: a misoriented substrate; and ann-AlGaInP cladding layer, an active layer and p-AlGaInP cladding layerwhich are formed above the substrate. The p-AlGaInP cladding layer has aridge structure having a substantially symmetrical shape, and currentblocking layers are formed on both sides of the ridge structure.

In one embodiment of the present invention, the p-AlGaInP cladding layerhas a p-AlGaInP first cladding layer, a p-AlGaInP second cladding layerand an etching stopper layer formed between said first cladding layerand said second cladding layer.

In one embodiment of the present invention, a layer for monitoring anetched amount of the p-AlGaInP second cladding layer is formed withinthe p-AlGaInP second cladding layer.

In one embodiment of the present invention, the tapered shape is suchthat the width of the tip portion is narrower than that of the laserunit, and a width of a tip of the tip portion is about 1 μm or less.

In one embodiment of the present invention, the tapered shape is suchthat the width of the tip portion is wider than that of the laser unit.

Thus, the invention described herein makes possible the advantages of(1) providing a dry-etching method which is performed on a III-V groupand II-VI group compound semiconductors and, furthermore, on a III-Vgroup compound semiconductor containing Al by using a chlorine gas addedwith a nitrogen gas, and is capable of obtaining a verticalcross-section and a smooth etching surface without reducing theproduction amount of chlorine gas radicals, and of (2) providing asemiconductor laser device fabricated by using this dry-etching methodand a production method thereof.

These and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an ECR-RIBE (Electron CyclotronResonance-Reactive Ion Beam Etching) apparatus;

FIGS. 2A and 2B are cross-sectional views of InP after the dry-etchingaccording to one embodiment of the present invention;

FIG. 3 is a cross-sectional view of InP after the dry-etching accordingto one embodiment of the present invention;

FIG. 4 is a cross-sectional view of InP after the dry-etching accordingto one embodiment of the present invention;

FIG. 5 is a cross-sectional view of InP after the dry-etching accordingto one embodiment of the present invention;

FIG. 6 is a cross-sectional view of InP after the dry-etching accordingto one embodiment of the present invention;

FIG. 7 is a structural cross-sectional view of a spin-etching apparatusfor uniformly performing wet-etching while rotating the substrate;

FIG. 8 is a cross-sectional view of InP after the dry-etching accordingto one embodiment of the present invention;

FIG. 9 is a structural cross-sectional view of a dry-etching apparatusincluding a radical beam source, an ion beam source and an ECR source;

FIGS. 10A, 10B and 10C are cross-sectional views of a laser diode withmode size converter according to one embodiment of the presentinvention;

FIGS. 11A to 11G are cross-sectional views illustrating the productionsteps for the laser diode with mode size converter shown in FIGS. 10A,10B and 10C;

FIG. 12A, 12B and 12C are cross-sectional views illustrating a doublestage dry-etching including different conditions according to oneembodiment of the present invention;

FIGS. 13A to 13D are cross-sectional views illustrating the productionsteps for a semiconductor laser according to one embodiment of thepresent invention;

FIGS. 14A and 14B are cross-sectional views of a semiconductor laser forcomparing ridge symmetry;

FIGS. 15A and 15B are cross-sectional views of a semiconductor laserincluding a layer monitoring an etching amount in the cladding layer;and

FIG. 16 is a graph showing a result of optical emission spectroscopy ofplasma.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will bedescribed in detail.

(EXAMPLE 1)

As a first embodiment of dry-etching according to the present invention,dry-etching on a III-V group compound semiconductor will be described. Asample to be etched is InP, and a chlorine gas and a nitrogen gas areused as the etching gases.

FIG. 1 schematically illustrates the construction of an ECR-RIBEapparatus (Electron Cyclotron Resonance-Reactive Ion Beam Etchingapparatus; hereinafter, referred to as an ECR-RIBE apparatus) which isused in the present embodiment. In this apparatus, the sample to beetched is positioned outside of coils which generate a magnetic field.

As illustrated in FIG. 1, the ECR-RIBE apparatus includes an ECR source101, a reaction chamber 102 which accommodates the sample and isconnected to the ECR source 101, and an exhaust pump system (not shownin the figure). The ECR source 101 generates ions or radicals. Achlorine gas and a nitrogen gas whose flow rates are placed undercontrol are introduced into the ECR source 101 through a gas inlet 108.Furthermore, a microwave of 2.45 GHz is guided into the ECR source 101through a waveguide tube 106 toward a quartz window 107 so that thechlorine gas and the nitrogen gas become exited. Electrons resonate dueto the magnetic field of 875 gausses generated by the coils 103, andengage in circular motion thereby repeating collisions with the gasmolecules. Chlorine ions and nitrogen ions thus created in the ECRsource 101 are accelerated by a grid 104, and are radiated onto thesample 105.

Although the chlorine ions and the nitrogen ions are accelerated andradiated onto the sample 105, since the chlorine radicals and thenitrogen radicals created in the ECR source 101 are not ionized, theyare not accelerated. However, the chlorine radicals and the nitrogenradicals reach the surface of the sample 105 by diffusion, andcontribute to the etching. This ECR-RIBE apparatus differs from anECR-RIBE apparatus with auxiliary coil reducing a divergence of magneticfield in that the coils 103 are not provided on the side of the reactionchamber 102. For this reason, a magnetic field generated by the coils103 is a diverging magnetic field.

Ions and radicals created as described above reach the surface of thesample 105, and react with InP of which the sample is made to yield anIn chloride and a P chloride. The boiling point of a P chloride is low,and it is readily vaporized. For example, the boiling point is 76° C.for PCl₃ and 162° C. for PCl₅.

On the other hand, the boiling point of an In chloride is high, and ittakes effort to vaporize it. For example, the boiling point is 560° C.for InCl₂ and 600° C. for InCl₃. Therefore, a layer of In chloride isformed on the surface of the sample 105. Since the vaporization of Inchloride is facilitated by collisions of the accelerated chlorine andnitrogen ions from the ECR source 101 onto the surface of the sample105, an acceleration voltage for the ions is an important factor. At 300V or below, the In chloride is not vaporized, and the sample is notetched.

Table 1 shows etching conditions for the present embodiment.

                                      TABLE 1                                     __________________________________________________________________________                Microwave                                                                           Accelerating                                                                        Internal                                                                           Sample                                             Chlorine Nitrogen power voltage pressure temperature                        __________________________________________________________________________    3˜20                                                                          3.5˜35                                                                        200W  300˜900                                                                       0.5˜2.5                                                                      Room temperature                                   SCCM SCCM (Fixed) V mTorr -300° C.                                   __________________________________________________________________________

Under the conditions shown in Table 1, the etching yields the optimumresult with the acceleration voltage equal to about 300 V or above. Amask used in the above etching is made of SiO₂.

Hereinafter, results of the dry-etching performed under the conditionsshown in Table 1 will be described.

As an experiment, dry-etching was performed with a chlorine flow ratebeing about 10 SCCM, an acceleration voltage being about 650 V, aninternal pressure during reaction being about 2.5 mTorr and a sampletemperature being about 200° C., while a nitrogen flow rate is varied.The evaporation of a III group compound can be facilitated by heating asample support and keeping a sample temperature at about 200° C.

FIGS. 2A, 2B, 3 and 4 schematically illustrate cross-sections of InPperformed with dry-etching. FIGS. 2A, 3 and 4 correspond to the nitrogenflow rates of about 35 SCCM, about 7 SCCM and about 3.5 SCCM,respectively. As can be seen from these figures, although a part of InPis etched away, the bottom surface (etching surface) comes out to beextremely rough. FIG. 2B is a perspective view of FIG. 2A. FIG. 2B alsoshows that the bottom surface is rough. In FIG. 3, the sample is etchedin a substantially perpendicular direction with respect to the SiO₂mask, and the surface roughness almost disappears. In FIG. 4, there isno surface roughness, and the etching surface is smooth. However,side-etching where a portion under the mask is also etched away occurs,and the sample is not etched in the perpendicular direction with respectto the mask.

From the above results, there seems to be a boundary of whether or notthe etching surface becomes rough between the chlorine/nitrogen flowrate ratio of about 0.29 and about 1.43. By conducting experiments, itwas determined that the boundary of the chlorine/nitrogen flow rateratio was in the vicinity of about 1.0. Also found was that the bestsmoothness of the etching surface was obtained when thechlorine/nitrogen flow rate ratio was in the vicinity of about 2.85.

However, the cross-section illustrated in FIG. 4 does not have verticalsides, showing that substantial side-etching occurred. Therefore, inorder to obtain vertical sides, it is necessary to reduce chemicalreaction components during the dry-etching. Then, dry-etching wasperformed with the sample temperature being reduced to about 100° C. Theremaining conditions other than temperature were the same as in the caseof FIG. 4. The result is illustrated in FIG. 5.

By reducing the sample temperature to 100° C., a sputtering componentbecomes stronger than a chemical reaction component, and the SiO₂ maskretreats to the substrate side by etching. This results in over-etching,and the cross-sectional shape becomes trapezoidal. However, since theetching surface is very smooth, no practical difficulty arises with thetrapezoidal cross-section.

As can be seen from FIGS. 4 and 5, when the chemical reaction componentis predominant over the sputtering method in etching, the side-etchingoccurs. When the sputtering component is predominant over the chemicalreaction component, the mask retreats and over-etching results.

Next, etching conditions for obtaining vertical sides in a cross-sectionwill be considered, and the result thereof will be described.

The etching was performed with a sample temperature being about 150° C.so as to increase the chemical reaction component, and with a supply ofchlorine being increased up to about 11.5 SCCM so as to improve theetching rate (the nitrogen flow rate is 3.5 SCCM, which is the same asin FIG. 4). The result is illustrated in FIG. 6. As can be seen fromFIG. 6, the sputtering component and the chemical reaction component areproperly balanced, and a cross-section having vertical sides isrealized. In this case, the acceleration voltage is kept at about 650 V,and the internal pressure is kept at about 2.5 mTorr.

The etching conditions for each of the cases illustrated in FIGS. 2A and2B, 3, 4, 5 and 6 are shown in Table 2.

                                      TABLE 2                                     __________________________________________________________________________                            Accelerating                                                                        Internal                                                                          Sample                                        Chlorine Nitrogen Chlorine/Nitrogen voltage pressure temperature                                               (SCCM) (SCCM) flow rate ratio (V)                                            (mTorr) (° C.)                       __________________________________________________________________________    FIG. 2A,2B                                                                          10   35   0.29    650   2.5 200                                           FIG. 3 10 7 1.43 650 2.5 200                                                  FIG. 4 10 3.5 2.8 650 2.5 200                                                 FIG. 5 10 3.5 2.8 650 2.5 100                                                 FIG. 6 11.5 3.5 3.29 650 2.5 150                                            __________________________________________________________________________

If the chlorine/nitrogen flow rate ratio is equal to about 1 or greater,then the etching surface does not become rough. However, if this flowrate ratio is made equal to or greater than 6.4, then the etchingsurface starts to become rough again. Taking the roughness of etchingsurface into consideration, the optimum value for the chlorine/nitrogenflow rate ratio is in the range of about 1.0 to about 6.4.

FIG. 16 shows a result of optical emission spectroscopy of plasma. Thisspectroscopic result shows changes in intensities of nitrogen ions,chlorine ions and chlorine radicals with respect to the nitrogenconcentration. Each of the optical emission intensities shown in FIG. 16is normalized with the optical emission intensity of plasma of achlorine gas only. Optical emission is observed at 652 nm for thenitrogen ions, 450.8 nm for the chlorine ions and 727.9 nm for thechlorine radicals. Optical emission at 652.9 nm in the case of chlorinegas only is a noise, not the optical emission due to the nitrogen ions.

The optical emission intensity of nitrogen ions monotonically increasesas the added amount of nitrogen increases. Although the optical emissionintensity of chlorine ions increases with the addition of nitrogen, itreaches the maximum value when the added concentration of nitrogenbecomes about 23%. This maximum value is about 1.4 times the value withno nitrogen being added. Then, the optical emission intensity slightlydecreases as the added concentration of nitrogen increases, and becomessaturated at the value about 1.3 times the value with no nitrogen beingadded. The optical emission intensity of chlorine radicals increases byabout 10% when the nitrogen is added, but becomes saturated at thisvalue. Further addition of nitrogen does not result in any increase ofthe optical emission intensity.

Hereinafter, changes in the above-described optical emission intensitieswill be described in comparison with etching characteristics.

A case where the chlorine/nitrogen flow rate ratio is less than 1corresponds to a portion of FIG. 16 where the nitrogen concentrationexceeds 50% (region 1). In region 1, although the chlorine ion intensityis about 1.3 times the value with pure chlorine (no nitrogen added), thenitrogen ion intensity is about 3 times the value with pure chlorine.That is, due to excessive nitrogen ions, the P chloride, which has avapor pressure higher than the In chloride, are considered to beselectively sputtered, thereby making the etching surface rough.

A case where the chlorine/nitrogen flow rate ratio is between about 1and about 6.4 corresponds to a portion of FIG. 16 where the nitrogenconcentration is between about 13% to about 50% (region 2). In thisregion, the nitrogen ion intensity has not increased very much. Thedesorption from the surfaces of In chloride and P chloride are properlybalanced, thereby realizing a smooth etching surface.

A case where the chlorine/nitrogen flow rate ratio exceeds 6.4corresponds to a portion of FIG. 16 where the nitrogen concentration isless than about 13% (region 3). In region 3, the etching surface becomesrough again. The reason is considered to be as follows. Since thedesorption of In chloride and P chloride which are generated occursmainly due to thermal energy rather than the sputtering effect,selective desorption of the P chloride occurs.

As described above, a substantial feature of the present invention isthat the effect of adding the nitrogen gas is not only to facilitate thecreation of chlorine ions but also to facilitate the desorption of IIIgroup or V group chlorides because of the sputtering effect of thenitrogen ions themselves. This is also true when the present inventionis applied to a II-VI group compound semiconductor.

Although, in the above description, InP which is a III-V group compoundsemiconductor is used as a sample to be etched, a compound semiconductorof AlGaInP type or AlGaInN type, or a II-VI group compound semiconductorof ZnMgSSe type can also be used in place of the InP as described below.Moreover, the etching can be performed with the substrate being kept ata room temperature although the etching rate decreases.

(EXAMPLE 2)

Hereinafter, a dry-etching method for a III-V group compoundsemiconductor will be described as a second embodiment of thedry-etching method according to the present invention. Specifically, inthis dry-etching method, only a sample surface is heated for etching bykinetic energy of accelerated ions without raising a temperature of theoverall sample.

In the present example, InP is used as an etching sample, and SiO₂ isused as an etching mask. The method described in this example can beapplied to an etching of a II-VI group compound semiconductor.

As described in the above Example 1, if a sample temperature is raised,then the chemical reaction component during dry-etching becomespredominant over the sputtering component, and the side-etching occurswhere a portion under the mask is also etched away. However, if thesample temperature is lowered, then the sputtering component becomesstrong, and the over-etching where the mask retreats occurs or theetching surface becomes rough.

Accordingly, in the present embodiment, the sample is closely attachedto a sample holding jig fixture made of Al, and the etching is performedwhile this jig fixture is being cooled.

Ions created in the ECR source are accelerated by the grid with thevoltage of several hundreds V. The ions which have thus acquired kineticenergy are then radiated onto the sample. Radicals created in the ECRsource are not accelerated. Although energy for one radical is as smallas 20 to 30 eV, since the number of radicals created is large, the totalenergy received by the sample surface from the radicals aresubstantially large. Since the sample surface receives energy of anumber of ions and radicals as described above, the same effect asheating the sample itself to a temperature of several hundreds degreesCelsius is obtained without actually raising the temperature of thesample. That is, by heating the surface of the sample as such,evaporation of a III group or II group chloride is facilitated, therebyimproving the etching rate.

FIG. 8 illustrates a cross-section of the InP sample when dry-etching isperformed on the sample by using an ECR-RIBE apparatus, with thechlorine flow rate being about 11.5 SCCM, the nitrogen flow rate beingabout 3.5 SCCM, the microwave power being about 200 W, the internalpressure being about 2.5 mTorr and the acceleration voltage being about650 V.

In this dry-etching, the sample is not heated as a whole. The sample isheld by a sample holding jig fixture made of Al, which is mounted on aliquid-cooled sample support. Because of this construction, only aportion of the sample in the vicinity of the surface is heated while thetemperature in other portions does not increase, thereby protecting thesample from thermal damage. Doing so is particularly effective inetching a sample including a II-VI group compound because the crystalgrowth temperature of a II-VI group compound semiconductor is low (about260° C.) and it is therefore necessary to keep the etching temperaturelower than the crystal growth temperature (about 250° C. or less) inorder to prevent the crystallinity of the sample from deteriorating.

As described in the above Example 1, the shape of the cross-section ofthe etched sample reflects a balance of the sputtering component and thechemical reaction component during etching. That is, if the sputteringcomponent is predominant, then the sample is over-etched, and if thechemical reaction component is predominant, then side-etching results.

As can be seen from FIG. 8, according to the present embodiment, thecross-section of the sample has substantially vertical sides, indicatinga proper balance of the sputtering component and the chemical reactioncomponent, although the overall temperature of the sample is around roomtemperature. The cross-section shown in FIG. 8 has substantially thesame cross-sectional shape as in the case where etching is performedwith the sample temperature being set at about 150° C., i.e., as in thecase shown in FIG. 6. That is, as far as a cross-sectional shape isconcerned, the result shown in FIG. 8 where etching is performed withoutheating the sample is the same as the result shown in FIG. 6 whereetching is performed with the sample temperature being set at about 150°C. The etching rate in the case of FIG. 8, however, is lower than thatin the case of FIG. 6 by about 25%.

In the present embodiment, although the sample temperature is set aroundroom temperature, it is also possible to reduce the difference in thedegree of sublimation between a V group chloride and a III groupchloride by cooling the sample support to 0° C. or below such that thesublimation of the V group chloride is inhibited. This makes it possibleto perform dry-etching which is capable of obtaining a sample having across-section with vertical sides and a smooth etching surface.

(EXAMPLE 3)

As a third embodiment of a dry-etching according to the presentinvention, a dry-etching on a III-V group compound semiconductor will bedescribed. Specifically, a dry-etching where double-stage etching withdiffering conditions is performed will be described. In this etching,InP and SiO₂ are used as a sample and an etching mask, respectively, andchlorine and nitrogen are used as an etching gas.

First dry-etching is performed by using an ECR-RIBE apparatus. In thisfirst dry-etching, the internal pressure is set at about 1 mTorr or lessand the acceleration voltage is set at about 300 V or greater so thatcollisions among gas molecules are inhibited, thereby making the iondensity larger than the radical density. The chlorine/nitrogen flow rateratio is set at about 1 or greater, and the sample temperature is set atabout 100° C. In this dry-etching, etching due to the sputteringcomponent becomes predominant over etching due to the chemical reactioncomponent, and fast dry-etching proceeds in the direction perpendicularto the sample surface, thereby forming a shape close to a desired shape.

The above-described first dry-etching has a relatively high etching rateof about 1000 Å/minute. When etching is performed at high speed, adefect may result on the etching surface including the side and bottomsurfaces, or the etching surface may become rough. This is becausehalogen ions created in the ECR source are accelerated by high voltagesof 300 V or greater, and are radiated onto the sample, thereby creatinga crystalline defect in the sample. It is also because, since theboiling point of a halogen compound differs for a III group (or IIgroup) and a V group (VI group), the stoichiometry becomes misaligned atthe etching surface, resulting in a larger amount of the III group (orII group) element than the V group (or VI group) element at the etchingsurface.

Next, following the first dry-etching, a second dry-etching isperformed. One purpose of the second dry-etching is to remove a layerincluding fabrication-induced damage occurred during the firstdry-etching. It is also a purpose of the second dry-etching to removesurface roughness from the etching surface in order to obtain a smoothsurface in the event such surface roughness has resulted on the etchingsurface. In order to achieve the above goals, the second dry-etching isperformed with the chlorine/nitrogen flow rate ratio being set at about3 or greater, the internal pressure at about 2 mTorr or greater, theacceleration voltage at about 300 V or less and the sample temperatureat about 200° C. In this dry-etching, the number of collisions among gasmolecules increases, and the radical density becomes larger than the iondensity. Furthermore, since the mean free path becomes short, thechemical reaction component acts stronger than the sputtering component.

In the above-described dry-etching under conditions for strongerchemical reaction component, since the fabrication-induced damage to thecrystals is small, a layer including many fabrication-induced damagescan be removed in the first etching. If the surface roughness occurs onthe etching surface in the first dry-etching, the etching surfaceincluding the surface roughness can be smoothed.

The first dry-etching can be performed with the following conditions:chlorine/nitrogen flow rate ratio≧about 1; internal pressure≦about 1mTorr; and acceleration voltage≧about 300 V. However, the following ispreferable for the optimum conditions: chlorine flow rate/nitrogen flowrate≧about 3; internal pressure≦about 0.5 mTorr; and accelerationvoltage≧about 600 V.

The second dry-etching can be performed with the following conditions:chlorine/nitrogen flow rate ratio≧about 3; internal pressure≧about 2mTorr; and acceleration voltage≦about 300 V. However, the following ispreferable for the optimum conditions: chlorine flow rate/nitrogen flowrate≧about 10; internal pressure≧about 3 mTorr; and accelerationvoltage≦about 100 V.

FIGS. 12A, 12B and 12C are cross-sectional views illustrating the stepsof dry-etching according to the present embodiment. First, asillustrated in FIG. 12A, a patterned SiO₂ mask 1202 is formed on an InPsubstrate 1201. Then, as illustrated in FIG. 12B, the first dry-etchingis performed. This first dry-etching creates a damaged layer 1203induced by the fabrication on the etching surface. Next, as illustratedin FIG. 12C, the second dry-etching is performed. In the seconddry-etching, the chlorine ion density is smaller and the chlorineradical density is larger than in the first dry-etching. By performingthe second dry-etching, the damaged layer 1203 induced by thefabrication is removed, and a smooth etching surface including sidesperpendicular to the mask 1202 can be formed.

In the above description, relative magnitudes of the chlorine iondensity and the chlorine radical density with respect to each otherduring the first dry-etching and the second dry-etching are varied bychanging the internal pressure, the flow rate and the accelerationvoltage. Alternatively, the first dry-etching and the second dry-etchingcan be performed with only the acceleration voltage being varied. Thatis, while the conditions, namely the chlorine/nitrogen flow rateratio≧about 3, the internal pressure≧about 2 mTorr and the sampletemperature at about 200° C., are applied to both the first dry-etchingand the second dry-etching, the acceleration voltage is set at about 900V for the first dry-etching and at about 100 V for the seconddry-etching. Even with dry-etching under such conditions, an etchingsurface which has no roughness can be realized.

(EXAMPLE 4)

Hereinafter, etching on a III-V group compound semiconductor will bedescribed as a fourth embodiment of an etching method according to thepresent invention. Specifically, an etching method where double-stageetching including dry-etching and wet-etching is performed will bedescribed. In this etching, InP and SiO₂ are used as a sample and anetching mask, respectively, and chlorine and nitrogen are used as anetching gas. As an etchant for the wet-etching, hydrochloric acid,acetic acid and hydrogen peroxide are used.

First, the first etching (dry-etching) will be performed by using anECR-RIBE apparatus. This first etching is performed under followingconditions: the chlorine flow rate/nitrogen flow rate≧about 1; theinternal pressure is greater than about 2 mTorr; the accelerationvoltage is greater than about 300 V; and the sample temperature isgreater than about 100° C. Although it is possible to perform the firstetching under the above conditions, the optimum conditions are asfollows: the chlorine flow rate is about 11.5 SCCM; the nitrogen flowrate is about 3.5 SCCM; the sample temperature is about 150° C; theacceleration voltage is about 650 V; and the internal pressure is about2.5 mTorr. The sample can be fabricated into a predetermined shape underthe above conditions. A layer with a fabrication-induced damage which iscreated in the first etching is removed by the second etching, whichwill be described in the following.

FIG. 7 schematically illustrates a structure of a spin-etching apparatusused in the second etching. The second etching, that is, the wet-etchingis performed inside a reaction chamber 705. The sample 701 which wassubjected to the above dry-etching is placed on a sample holder 702. Thesample holder 702 holds the sample 701 by a vacuum chuck and rotates ata predetermined rate of rotation. A mixture of hydrochloric acid, aceticacid and hydrogen peroxide, which is stored in an etchant tank 704 andis kept at a predetermined temperature, is discharged through a nozzle703 and falls onto the sample 701. The nozzle 703 makes a reciprocatingmotion of predetermined distance in the radial direction passing throughthe center of the sample holder 702. The reciprocating motion of thenozzle 703 in the radial direction, which drops the etchant onto therotating sample 701, allows extremely uniform wet-etching to beperformed. Accordingly, the damaged layer induced by the fabricationcreated in the first etching is removed. The mixing ratio of thehydrochloric acid, the acetic acid and the hydrogen peroxide is 3:36:1,and the temperature of the mixture is kept at about 20° C.

Since the wet-etching does not include sputtering component, even asmall damage which is created by dry-etching can be prevented by usingthe wet-etching. This improves the smoothness of the etching surface.

Although, in the present embodiment, the mixture of hydrochloric acid,acetic acid and hydrogen peroxide is used as the etchant for the secondetching, a mixture of sulfuric acid, hydrogen peroxide and water, amixture of hydrochloric acid and phosphoric acid, or a mixture ofsaturated bromine water and methanol can alternatively be used as theetchant as long as the etchant is capable of removing the damaged layerinduced by the fabrication created in the first etching.

(EXAMPLE 5)

Hereinafter, in addition to the ECR source, a dry-etching apparatusincluding a radical beam source and an ion beam source and a method ofdry-etching using this dry-etching apparatus will be described.

FIG. 9 schematically illustrates a structure of a dry-etching apparatusof the present embodiment. This apparatus includes a radical beam source902 and an ion beam source 903 in addition to the ECR source 904 and thereaction chamber 901. The radical beam source 902 and the ion beamsource 903 are connected to the reaction chamber 901.

The reaction chamber 901 includes therein a sample holder 905 whichholds a sample 906. Chlorine radicals produced in the radical beamsource 902; chlorine ions produced in the ion beam source 903; andchlorine ions, chlorine radicals and nitrogen ions produced in the ECRsource 904 are radiated onto the sample. The sample 906 is transferredfrom a load lock chamber 900, which is intended for a transfer of thesample 906 to the reaction chamber 901, to the reaction chamber 901. Anexhaust system (not shown in the figure) is maintained at about 10⁻⁶Torr or less.

In the radical beam source 902, a RF high frequency wave is added to thechlorine gas which then becomes a plasma. This produces the chlorineions and the chlorine radicals. Since the chlorine ions have a mean freepath of several cm when not accelerated, they collide with other atomsand electrons inside the radical source 902 or the reaction chamber 901,and become annihilated. Therefore, the chlorine ions do not reach thesample. The produced radicals reach the surface of the sample bydiffusion, and contribute to reaction.

Similarly, a RF high frequency wave is added to the chlorine gas insidethe ion beam source 903 which then becomes a plasma. This produces thechlorine ions and the chlorine radicals. By changing voltage applied toan extraction electrode 9031, a ratio of chlorine ions and chlorineradicals drawn from the ion beam source 903 can be changed. This is donesuch that the chlorine ions are drawn in an amount larger than thechlorine radicals so as to be radiated onto the sample surface.

As described in Example 1, the gas is decomposed and ions and radicalsare produced inside the ECR source 904. In this example, a nitrogen gasis introduced into the ECR source 904.

By including the ion source, the radical source and the ECR source asdescribed above, the radical density which is associated with thesmoothness and the ion density which is associated with the etching ratecan be controlled independently. For this reason, fast etching ispossible while maintaining the smoothness on the etching surface. Italso becomes easy to control the etching rate, the cross-sectional shapeand the smoothness on the etching surface. When dry-etching is performedon InP with a mixed gas of chlorine and nitrogen with SiO₂ being used asa mask, since a P chloride is readily sublimated but a In chloride isnot as described in Example 1, a layer of the In chloride is formed onthe surface of the sample. In order to sublimate this In chloride layer,kinetic energy of accelerated chlorine ions and nitrogen ions can beused.

Accordingly, the flow rate of the chlorine ions is made larger than thatof the chlorine radicals, and the chlorine ions and the nitrogen ionsare accelerated by high voltage of about 300 V or greater, and thensupplied. In order to have high etching rate, the temperature of thesample is set at about 150° C. or greater.

According to the present example, dry-etching on InP which results in asmooth etching surface can be performed under the following conditions:the chlorine radical flow rate from the radical beam source is about 1SCCM or greater; the chlorine ion flow rate from the ion beam source isabout 10 SCCM or greater; the accelerating voltage is about 300 V orgreater; and the nitrogen ion flow rate from the ECR source is about 3SCCM or less. Furthermore, dry-etching which results in a crosssectionhaving vertical sides and in a smooth etching surface can be realizedunder the following conditions: the chlorine radical flow rate is about1 SCCM; the chlorine ion flow rate is about 10 SCCM; the acceleratingvoltage for chlorine ions is about 600 V or greater; the nitrogen flowrate from the ECR source is about 3 SCCM; and the sample temperature isabout 150° C.

(EXAMPLE 6)

Hereinafter, a method for producing a semiconductor laser device usingthe etching method described in the above Examples 1 to 5 will bedescribed. A laser diode with mode size converter will be described inthis example. FIGS. 10A, 10B and 10C are cross-sectional viewsschematically illustrating a structure of the laser diode with mode sizeconverter.

This laser diode with mode size converter includes a laser unit 1010 anda mode size converter unit 1011 (a tip portion) as shown in FIG. 10A.The laser unit 1010 has a stripe shape of a constant width andthickness. The mode size converter unit 1011 has a tapered shape whosewidth reduces into an emitting facet 1012. The spot radius (mode radius)of the laser light is converted from the spot radius of the laser unit1010 to the radius m of the emitting facet 1012 (a tip of the tipportion 1011) as the laser light is guided through the mode sizeconverter unit 1011. The emitting facet has a width m of about 1 μm orless (typically about 0.6 μm), and the angle of the cross-section isabout 90° C.

FIG. 10B is a cross-section taken along a line A-A' in FIG. 10A. Asillustrated in FIG. 10B, an n-InP layer 1002, an n-InGaAsP claddinglayer 1003, an active layer 1004, a p-InGaAsP cladding layer 1005 and ap-InP cap layer 1007 are epitaxially grown in this order on an n-InPsubstrate 1001. These layers constitute a mesa stripe (a ridge stripe)1014, which is buried in semi-insulating InP 1006. A p-side electrode1009 is formed on the p-InP cap layer 1007, and an n-side electrode 1008is formed on the entire rear surface of the substrate 1001.

Positive holes injected from the p-side electrode 1009 recombine withelectrons injected from the n-side electrode 1008 in the active layer1004. Generation of light occurs under the p-side electrode 1009, andthe light thus generated is confined between the resonator end surfacesfor laser oscillation.

FIG. 10C is a cross-section taken along a line B-B' in FIG. 10A. As canbe seen from a comparison of FIGS. 10B and 10C, the width of the activelayer 1004 differs for the laser unit 1010 and for the mode sizeconverter unit 1011. That is, the width of the active layer 1004 issmaller for the mode size converter unit 1011.

Hereinafter, a method for producing a laser diode with mode sizeconverter will be described with reference to FIGS. 11A to 11G. FIGS.11A to 11G are cross-sectional views schematically illustrating thelaser unit 1010. The mode size converter unit 1011 differs only in thewidth of the active layer, and is produced at the same time as the laserunit 1010.

First, as illustrated in FIG. 11A, an n-InP layer 1102, an n-InGaAsPcladding layer 1103, an active layer 1104 and a p-InGaAsP cladding layer1105 are grown in this order on an n-InP substrate 1101 by Metal OrganicVapor Phase Epitaxy (MOVPE). Then, as illustrated in FIG. 11B, an SiO₂mask 1106 having a predetermined shape is formed on the p-InGaAsPcladding layer 1105.

Next, as illustrated in FIG. 11C, a mesa stripe (ridge stripe) 1109 isformed by using a magnetic field type ECR-RIBE apparatus in any one ofthe etching methods described in Examples 1 to 5 above. Etchingconditions are as follows: the chlorine/nitrogen flow rate ratio≧1; themicrowave power is about 200 W; the internal pressure about 2 mTorr orgreater; the sample temperature is about 150° C. or greater; and theacceleration voltage is about 300 V or greater. With the mesa stripeformed under these conditions, an angel θ formed by the side surface ofthe mesa stripe and the surface of the substrate 1101 as shown in FIG.11G is in the range between about 60° and about 90°. Next, as shown inFIG. 11D, crystal growth is performed by MOVPE with the SiO₂ mask 1106being used as a mask for selective growth, thereby burying the mesastripe 1109 with the semi-insulating InP 1107. After removing the SiO₂mask 1106, as illustrated in FIG. 11E, the p-InGaAsP cap layer 1108 isformed by MOVPE. Finally, as illustrated in FIG. 11F, the p-sideelectrode 1111 and the n-side electrode 1110 are deposited, and thenheat treatment is performed so as to form ohmic contacts.

As described above, according to the present invention, by performingetching with the chlorine gas and the nitrogen gas in the ECR-RIBEapparatus, both the mesa stripe whose side forms an angle θ of about 60°to about 90° with the surface of the substrate 1101 and a cavity andwaveguide having an emitting facet whose width is about 1 μm or less canbe formed. According to the method of the present invention, an invertedmesa (the angle θ being greater than 90°) which reduces the reliabilityof the device can be avoided.

Although the laser diode is tapered such that the width of the tipportion is smaller than that of the laser unit in the above description,it should be appreciated that the width of the tip portion may be madelarger than that of the laser unit.

Although an ECR-RIBE apparatus is used in the above embodiments, adry-etching apparatus including an inductively coupled plasma source, adry-etching apparatus including a helicon plasma source, or dry-etchingapparatus including an NLD type plasma source can also be used.

Although the above embodiments are described with InP being used as acompound semiconductor, other III-V group or II-VI group compoundsemiconductors can also be used. Although chlorine gas is used in theabove descriptions, gases including chlorine, bromine or iodine can alsobe used.

(EXAMPLE 7)

Hereinafter, a method for producing another semiconductor laser device,using any one of the etching methods described in above Examples 1 to 5,will be described with reference to FIGS. 13A to 13D. In the presentembodiment, a compound semiconductor to be etched contains aluminum(Al).

First, as illustrated in FIG. 13A, an n-GaAs buffer layer (not shown inthe figure), an n-Al_(x) Ga_(y) In_(1-x-y) P (0<x≦1, 0≦y≦1; hereinafter,referred to as AlGaInP) cladding layer 1302, a multi-quantum well activelayer 1303 made of an AlGaInP barrier layer and a GaInP well layer, ap-AlGaInP first cladding layer 1304, a GaInP etching stopper layer 1305(thickness: about 5 nm) and a p-AlGaInP second cladding layer 1306 areepitaxially grown in this order on an n-GaAs substrate 1301 by MOVPEmethod. The GaAs substrate 1301 is an off-substrate which is tilted byabout 10 degrees from a (100) surface in the [110] direction.

Next, in order to form a ridge, a patterned SiO₂ mask 1307 having awidth of about 4 μm and a thickness of about 0.5 μm is formed on thep-AlGaInP layer 1306.

Next, as illustrated in FIG. 13B, by using any one of the etchingmethods described in the above Examples 1 to 5, a ridge 1313 is formedwith the SiO₂ mask 1307 being used as an etching mask. As an etchingcondition, the flow rate is set at about 11 SCCM for chlorine and atabout 3.5 SCCM for nitrogen so that the chlorine/nitrogen flow rateratio becomes about 3.1. Other conditions are as follows: theacceleration voltage is about 650 V; the internal pressure is about 2.5mTorr; and the sample temperature is about 100° C. By performingdry-etching under such conditions, a trapezoidal ridge 1313 which ishorizontally symmetrical can be obtained.

Typically, etching using a misoriented substrate does not make the ridgeto be horizontally symmetrical as illustrated in FIG. 14B. Since thesubstrate is tilted from the (100) surface, in wet-etching using asulfuric acid based etchant, the inclination of the side becomes smallnear the bottom of the ridge, and the ridge becomes asymmetrical inshape. As a result, the injection of carriers into the active layer andthe optical confinement become non-uniform, and the transverse modebecomes unstable. This becomes particularly prominent when the laser isactuated at a high temperature.

Moreover, in an AlGaInP type semiconductor laser, in order to shortenthe wavelength of laser light, the tilt angle is made larger and larger.According to the present embodiment, as illustrated in FIG. 14A, byperforming dry-etching under the above conditions, the ridge 1412 whichis symmetrical in shape can be formed even when an off-substrate isused.

As illustrated in FIG. 13B, the dry-etching for making the ridge isstopped at the etching stopper layer 1305. The thickness of thep-AlGaInP second cladding layer 1306 to be removed by the dry-etching isabout 1.5 μm. Such a thick layer is first removed for about 1.3 μm bythe first dry-etching which has strong sputtering components asdescribed in Example 2, and then the remaining thickness of about 0.2 μmof p-AlGaInP is removed by the second dry-etching which has strongchemical reaction components. In this way, damage due to etching to thelayers below the etching stopper layer 1305 can be avoided.

Alternatively, as described in Example 3, a thickness of about 1.3 μm ofthe second cladding layer 1306 can be removed by the dry-etching havingstrong sputtering components, and then the remaining thickness of about0.2 μm of the second cladding layer 1306 can be removed by thewet-etching performed as the second etching.

After forming the ridge 1313, as illustrated in FIG. 13C, an n-GaAscurrent blocking layer 1309 which serves as an n-type burying layer isselectively grown using the SiO₂ mask 1307, and then the SiO₂ mask 1307is removed.

Next, as illustrated in FIG. 13D, a p-GaAs contact layer 1310 is grown.Finally, an n-side electrode 1311 is formed on the rear side of ann-GaAs substrate 1301, and a p-side electrode 1312 is formed on thecontact layer 1310, thereby completing the laser structure.

In the method for producing a semiconductor laser device of the presentembodiment, by setting the flow rate ratio of a halogen gas and anitrogen gas in the range of about 1.4≦chlorine flow rate/nitrogen flowrate≧about 4.0 when forming the ridge 1313, the angle θ formed with thebottom surface of the ridge 1313 and the side surface of the ridge 1313can be made to be in the range of about 60 degrees to 90 degrees. Itbecomes also possible to produce a semiconductor laser device having aridge shape with excellent symmetry even if an off-substrate is used.For this reason, the confinement of carriers in the active layer and theoptical confinement do not become non-uniform, and a semiconductor laserhaving excellent reliability and stable transverse mode can be obtained.Furthermore, according to the present embodiment, although the etchingis performed on a compound semiconductor containing Al, the etching ratedoes not decrease.

In the above description, in the step of performing the dry-etching thep-AlGaInP second cladding layer, a thickness of about 1.3 μm of theAlGaInP cladding layer is removed by the first dry-etching, and then theconditions are changed and the second dry-etching is performed. In orderto easily detect (monitor) that a thickness of about 1.3 μm of AlGaInPcladding layer has been removed, a GaInP layer 1500 (thickness: about 10nm) may be inserted at the desired location in the second AlGaInPcladding layer 1506 before the etching as illustrated in FIG. 15A.

Assuming that the GaInP layer 1500 is included, if etching is performedon the AlGaInP second cladding layer while spectroscopic analysis of theplasma is being performed, then the value of spectroscopic analysischanges when the etching proceeds to the GaInP layer 1500. The reason isthat the GaInP layer 1500 does not contain Al. This change makes itpossible to accurately detect that a thickness of about 1.3 μm of thesecond cladding layer has been etched away. Then, the etching conditionscan be changed for the second dry-etching as illustrated in FIG. 15B,and a remaining thickness of about 0.2 μm of the second cladding layeris etched away. This makes it possible to produce a semiconductor laserdevice which experiences less damage during etching and has excellentcontrollability and uniform characteristics.

According to the present embodiment, when Al is contained in the sampleto be etched, even though Al₂ O₃ is formed from residual moisture withinthe reaction chamber, the desorption of Al₂ O₃ by sputtering can befacilitated by increasing the production amount of chlorine ions withoutdecreasing the production amount of chlorine radicals. Moreover, thechlorine radicals react with Al so that desorption of Al in the form ofaluminum chloride occurs. This eliminates a problem that the samplebecomes unsusceptible to etching or the etching rate decreases.

According to the present invention, following effects are obtained.

By setting the chlorine/nitrogen flow rate ratio to be about 1 orgreater and the internal pressure to be about 1 mTorr or greater, thedry-etching on a III-V group and II-VI group compound semiconductorwhich yields a smooth etching surface can be performed.

Moreover, by performing dry-etching, using a dry-etching apparatusincluding a radical source and an ion beam source, while independentlycontrolling the chlorine ion density, the chlorine radical density andthe nitrogen ion density, the dry-etching on a III-V group and II-VIgroup compound semiconductor which yields a smooth etching surface canbe performed.

Various other modifications will be apparent to and can be readily madeby those skilled in the art without departing from the scope and spiritof this invention. Accordingly, it is not intended that the scope of theclaims appended hereto be limited to the description as set forthherein, but rather that the claims be broadly construed.

What is claimed:
 1. An etching method for performing dry-etching on a III-V compound semiconductor or a II-VI group compound semiconductor in a dry-etching apparatus comprising a plasma source for creating a plasma with density of about 10¹⁰ cm⁻³ or greater, using a mixed gas containing a gas including a halogen element and a gas including nitrogen and using an acceleration voltage of about 300 V or more, wherein:(a flow rate of the gas containing said halogen gas)/(a flow rate of said nitrogen gas)≧about 1; and a process pressure during etching reaction is about 1 mTorr or greater.
 2. An etching method according to claim 1, wherein ions created in said plasma source are accelerated, and a sample is etched by kinetic energy of said accelerated ions while a sample surface is being heated.
 3. An etching method according to claim 1, wherein: ions created in said plasma source are accclerated; only a portion of the sample containing a II-VI group compound in the vicinity of the surface is heated by kinetic energy of said accelerated ions; and a support for said sample is cooled.
 4. An etching method according to claim 1, wherein etching is performed while a sample holder is heated.
 5. An etching method according to claim 1, further comprising the steps of:performing a first dry-etching wherein ions created in said plasma source are accelerated by a first accelerating voltage; performing a second dry-etching, after said first dry-etching, wherein ions created in said plasma source are accelerated by a second accelerating voltage; wherein said second accelerating voltage is larger than said first accelerating voltage.
 6. An etching method according to claim 1, further including a step of performing wet-etching.
 7. An etching method according to claim 1, wherein said dry-etching apparatus comprises a radical beam source and an ion beam source, and a density of radicals created in said radical beam source and a density of ions created in said ion beam source are independently controlled.
 8. An etching method according to claim 1, wherein said compound semiconductor is formed of Al_(x) Ga_(y) In_(1-x-y) P (0<x≦1, 0≦y≦1).
 9. An etching method according to claim 8, wherein said compound semiconductor is formed above an off-substrate.
 10. An etching method for performing dry-etching on a III-V group compound semiconductor or a II-VI group compound semiconductor in a dry-etching apparatus comprising a plasma source for creating a plasma with density of about 10¹⁰ cm⁻³ or greater, using a mixed gas containing a gas including halogen element and a gas including nitrogen, comprising the steps of:performing a first dry etching with a halogen ion density being made larger than a halogen radical density; and performing a second dry-etching within a halogen ion density being made smaller than a halogen radical density.
 11. An etching method for performing dry-etching on a III-V compound semiconductor in a dry-etching apparatus comprising a plasma source for creating a plasma with density of about 10¹⁰ cm⁻³ or greater, using a mixed gas containing a gas including a halogen element and a gas including nitrogen and using an acceleration voltage of about 300 V or more, wherein:(a flow rate of the gas containing said halogen gas)/(a flow rate of said nitrogen gas)≧about 1; and a process pressure during etching reaction is about 1 mTorr or greater.
 12. The etching method according to claim 11, wherein ions created in said plasma source are accelerated, and a sample is etched by kinetic energy of said accelerated ions while a sample surface is being heated.
 13. The etching method according to claim 11, wherein etching is performed while a sample holder is heated.
 14. The etching method according to claim 11, further including a step of performing wet-etching.
 15. The etching method according to claim 11, wherein said dry-etching apparatus comprises a radical beam source and an ion beam source, and a density of radicals created in said radical beam source and a density of ions created in said ion beam source are independently controlled.
 16. The etching method according to claim 11, wherein said compound semiconductor is formed of AlxGayIn_(1-x-) P (0<x≦1, 0≦y≦1).
 17. The etching method according to claim 16, wherein said compound semiconductor is formed above an off-substrate. 